Dual-voltage vehicle electrical systems of this type are conventional in automotive engineering for example. Due to the increasing number of electric consumers, in many cases, one single voltage supply no longer suffices. Furthermore, the electric consumers used require higher operating voltage and/or higher electric power so that dual-voltage vehicle electrical systems with different voltage levels of 14V and 42V for example have been developed. It is also conventional to connect these vehicle electrical systems by way of a dc.-dc. converter so that they can be supplied via a common generator for example. A principle problem of such type dual-voltage vehicle electrical systems is that the electric consumers in the vehicle electrical system with the low voltage level have to be protected from static overvoltage conditions due to a short between the two vehicle electrical systems. This protection can be achieved for example in that the electric consumers in the vehicle electrical system with the low voltage level are provided with corresponding overvoltage protection elements that are designed to match the voltage in the other vehicle electrical system. The disadvantage of this arrangement is that all of the electric consumers used in vehicle electrical systems with a low voltage level would have to be modified.
It is an object of the present invention to provide a device and a method allowing a greater ease of protecting the electric consumers in the vehicle electrical system with the lower voltage level from overvoltage conditions due to the other vehicle electrical system.